Many position sensors use an AC excitation signal as a primary signal and generate position sense signals as secondary signals. Information corresponding to a position of an object (e.g., control surfaces in an aircraft, a stator in a motor system, etc.) is included in each of the position sense signals. There have been several techniques to extract the position information from the position sense signals generated by the position sensors.
In some examples based on a phase locked loop (PLL), the PLL is employed for adjusting an output of a voltage-controller oscillator (VCO) until it locks in frequency and phase to an input signal. Thus, the PLL may be sensitive to phase delays of the input signal to cause circuit instability. Also, the PLL is noisy due to the VCO running asynchronously with other signals on a circuit board.
In other examples using one or more diodes for rectifying and filtering signals or a phase sensitive demodulator, a plurality of filters are used to provide an average over multiple cycles of an input signal. However, some of the filters may have long time constants to improve accuracy to thus result in unwanted delays in the overall system.
In other examples using a demodulator based on a zero-cross detection circuitry, a half-wave average filter circuitry, and a precision-rectifier averaging circuitry for synchronous demodulation, the zero cross detection circuitry toggles input switches therein in phase with an AC excitation signal to allow them selectively to be connected to averaging filters of the half-wave average filter circuitry. The average filters generate signals with a small amount of ripple voltage at a modulation frequency. The output signals generated from the average filters may then be sampled by an analogue-to-digital converter (ADC) and mathematical calculations may be performed on the sampled signals to output a position signal by a processor based on a field-programmable gate array (FPGA) or digital signal processor (DSP). However, this implementation requires a relatively large number of circuits and components, and some of the circuits and components can serve as potential error sources. The averaging filters present a tradeoff between a ripple amplitude (e.g., error), a dynamic response, and a circuit complexity.
Thus, there is a need of a demodulation technique with an improved accuracy, greater reliability, and lowered size/weight.